Motoring dynamometer for engine testing



y 1948. M. P. WINTHER MOTORING DYNANQMETER FDR ENGINE TESTING Filed May 28, 1945 Patented July 13, 1948 UNITED STATES PATENT- OFFICE MOTORING DYNAMOMETER, FOR ENGINE TESTING Martin P. Winther, Waukegan, Ill., assignor to Martin P. Winther, trustee Application May 28, 1945, Serial No. 596,251

4 Claims. (Cl. 73-116) 2 This invention relates to electric apparatus, the bearings 3 for the limited distance required and with regard to certain more specific features, by the sca e movement. a to motor controls and associated dynamometers, Supported upon bearings I5 within the rockbrakes and the like. ing case 1 is a rotary shaft ll. Keyed to the Among the several objects of the invention may 5 shaft I1 is a toothed magnetic rotor IS. The

be noted the provision of a motored eddy-current et of the rotor are indicated at y ant dynamometer unit which, in addition to being as flux-concentrating poles.

useful for absorbing energy from a rim mover Fixed inside of the case I is a magnetic stator or the like, may be used to drive the prime mover 23 within which is located an annular electric either for starting or'testing urposes; the pmcoil 25 providing a toric flux field interlinking vision of a motored dynamouneter of the class dethe stator 23 and the rotor I9. Interlinkage is scribed which'may instantaneously be switched throu t teeth Within and attached to from load-absorbing to motoring test operation; e StetOl 33 e magnetic, eddy-Cu e t rings Tl the provision of apparatus of. the class described through wh h Said fi field p These es in which an eddy-current, power-absorbing or include suitable water-cooling passages 29. Thus braking element is controlled so as to function as if the coil 25 is excited, and the shaft l1 rotated, a governor determining a maximum motoring y currents Wil1 b engendered in e e y-eu speed; the provision of apparatus of this class rent rings 27, t generating t w ich is ca which is compensated for governor droop; and le O by t e Water circulated in the p ges 29.

the provision of apparatus of this class which is he magnetic field from the y currents simple to construct, control and maintain. Other acts W th t e fi from the Coil 25 W t resulting objects will be in part obvious and in part pointed torque applied to the rocking case E. The force out hereinafter. of this torque is applied to the scale l5 through The invention accordingly comprises the el the linkage II. From the scale reading suitable ments and combinations of elements, features of pu ati ma be made for sep wer deconstruction, and arrangements of parts which VelOped in any prime m c p e t0 S aft l will be exemplified in the structures hereinafter The action is effective in either direction of r described, and the sco e of the application of tation of the shaft l1. Hereinafter the entire which will be indicated in the following claims. e ergy-absorbing dy e ements indi- In the accompanying drawin s, i hi h one cated by the brackets shown in Fig. 1 will be reof various possible embodiments of the invention ferred to as A dynamometel element ch as is illustrated, D is incapable of turning or motoring shaft I'l. Fig. 1 is a schematic layout showing Wiring Further details of the unit D will be unnecessary, diagram and longitudinal s ti n through t inasmuch as these may be obtained from various mechanical elements of the invention; and, 35 U. S. patents on the subject, including 2, Fig. 2 is a fragmentary end elevation on a redated April 1 and dated October duced scale ofthe mechanical parts taken from 29, 1940- the right of Fig. 1. At M is generally shown a wound-rotor, induc- Similar reference characters indicate corretiOn mOtOr- The Stator 3| Of t motor is atsponding parts throughout the several vi of tached to the inside of the case 1. The stator the drawings, windings are indicated at 33. The rotor 35 is Referring now more particularly to Fig, 1, keyed to the shaft i1 and its windings are indithere are shown at numerals l pedestals carrying Gated a These windings through Shes 39, bearings 3 for gudgeons 5 of a dynamometer case Slip rmgs and Wlres 43 are connected with 1. This case rocks in the bearings 5 and, as outside adjustable stepped wire-wound reshown in Fig. 2, includes a torque arm 9 connected sistance or rheostat 45. Thus the induction motor M is a so-called wound-rotor slip-ring motor through a reversible linkage I I with a force rmeasuring scale l3. Further details of the reversible Wlth an outside resistance clrcmt for the rotor winding. The purpose of the adjustable resistlinkage H W111 not be gven Smce f we ance is to obtain suitable speed variations under mon on many dynamometers now in use, their various torque conditions. An A. C. circuit for purpose being simply to obtain e reading on the the stator windings as is shown at 41, the same scale I3 in either direction of force application, passing throu h a three-pole control switch 49 as determined by the moment of the arm 9. It and a three-pole line switch 5|. 111 be understood that the case 1 rocks freely in As is known, a wound-rotor motor such as M has a tendency either to speed up or slow down with a change in load. This is because most wirewound or grid rheostatic arrangements such as shown at 45 have definite steps. If two consecutive rheostat step adjustments produce a difierence of 100 R. P. M. in the motor speed, the Operator is unable to set the speed of the motor within this difference. Thus if the speed steps required by the rheostat are 800 to 900 R. P. M., an operator would be unable to set the speed of the motor at 850 R. P. M. Liquid rheostats might be used but these are very expensive, cumbersome and their upkeep is diilicult. By means of the present invention a precise motor speed may be more conveniently maintained, as will appear.

From the above it is clear that the motor unit M may be used to drive whatever engine or the like (under test) is attached to the shaft IT. This may be desirable, for example, for starting the engine or in order to make a friction test. The reaction of the motor stator ii on case 1 tends to apply a torque force to the scale I3. Thus, for example, friction horsepower may be determined.

An important advantage of the invention is that a ver quick switch may be made from operation of an engine as a prime mover delivering energy to the dynamometer D, to motoring or the engine from motor element M, under either of which conditions torque may be computed from suitable readings on the scale l3. This allows the engine tester for example to determine friction horsepower under substantially the same operating conditions as existed under a given power load on the engine.

In order to make quick changes from powerabsorbing conditions during which the dynamometer D is operative, to motoring conditions during which the motor M is driving, the circuit shown is used. This consists in an exciter circuit ll connected to the dynamometer coil 25. This exciter circuit 53 is served by a generator 55. The generator I! is driven at a constant speed from a motor it served by an A. C. line II.

The generator I! may be of any high-grade D. C. variety. The one shown is of the series type with -a teaser field exciter winding SI and a series field 51. the latter being in the exciter circuit 51 of the winding 2'. If desired, a third and separately excited field may be used for balancing out residual magnetism in the generator but since that is a detail having nothing to do with the invention per se, it is not described. Whether or not it is used depends upon the type of generator employed.

The winding 6| oi generator BI is connected with wires 3. Wires .3 are fed from a bridge rectifier 85 which may be of the electronic type or copper oxide type, the latter being shown for example. This rectifier is fed from an A. C. supply circuit the latter being supplied from the A. C. winding ll of a permanent magnet A. C. generator II. The latter is driven from the shaft II. The permanent magnet of this generator is and a part of said wire II. The voltages from the rectifiers 1! and II are in opposition.

Although both the rectifiers I! and I are indicated as being of the copper oxide type, it is to be emphasized that vacuum tube rectifiers may be used for either or both, as desired.

Part of the resistance ll may :be shunted out by means of a shunt circuit which is under control of element ll of a magnet switch .9. The amount of the resistance Ii adapted to be cut out by the shunt circuit II is variable. A second element SI of the switch ll controls an ignition circuit I of, for example, an internal combustion engine coupled to the shaft l1 and under test.

A magnet coil SI is fed from the circuit 41 by wires ll, 85, 91 and switch 98. Closing of the switch 89 will cause opening of the switch elements I1 and ll.

The switch 48 is under control of a magnet coil III also connected across the line 41 through said switch N. This is done through wires II, III, I", switch II and wire II.

An object of the invention is to use the eddycurrent absorption dynamometer D as a governor brake to provide a maximum for the speed obtained by the wound rotor motor M when the device is used for motoring an engine connected for test purposes to shaft II. This is the engine which has its ignition switch wired into the circuit I.

Assume that for test an engine is connected to shaft N. Main switch II is closed and control switch 99 is open. This allows closing of the ignition circuit 1, since element ll of switch 0! is closed. Switch ll is open. Let it be assumed that the test engine is operating, thus driving the shaft II. The A. C. generator II, through rectitler 65, supplies direct current for the exciter coil ll of generator 55. Generator ll then supplies direct current for energizing the coil II. Thus excitation of coil II increases with speed. The energization of coil 2 is controlled by adjusting the resistance II. Most of resistance II is shunted by circuit II, switch element I! being closed. Adjustment oi the resistance I3 functions to set the speed at which absorption tests are made. The motor M at this time is idle but is ready at any instant to drive the engine whenever the engine ignition and action of the dynamometer D are cut off. Thus an engine may be placed under a test load and operated so that under the load it attains its running temperature and other desired conditions andthen a quick change is made from energy-absorbing conditions to motoring conditions, for example. to perform a friction horsepower test.

Change over to motoring is made by closing the control switch 9!. This opens the ignition circuit I (see coil 03 and switch element ll) so that the engine will not run under its own power. This also has the instant effect of closing the switch I! (see coil III) as well as of opening the switch element 81. The control circuit then operates as follows:

The tendency is for direct current to fiow from the rectifier it through wire I8 and part of the adjustable resistance 13, then through the generator field ll via wires '3. Completion of this circuit is blocked at the rectifier 08 because the latter will not permit current to flow from its positive to its negative side. This amounts to the presence of a potential from rectifier I! to rectiher I. Thus so long as the voltage applied to the positive side of the rectifier II from wire 83 is higher than the positive voltage of the rectiiler II, no current will fiow through the generator field However, when the shaft speed ll is sumciently high to produce rectified D. C. po-

tential from the rectifier 65, which is higher than the potential in wires 63 from rectifier I9, current will fiow from the rectifier 65 through the generator field 6|, through the wires 63, resistance 13, returning to the negative side of the rectifier 65 via the resistance 15 and wire TI. Thus the rectifier 65 is the sole exciter for the enerator field 6|.

Rectifier l9 acts simply as a dam preventing fiow of current through the generator field 8| until suflicient voltage is obtained at rectifier 65 to overcome the selected reference voltage as determined by the resistance 13. The result is that while driving the dead engine from the motor M, acceleration may continue until the coil 6| begins to receive current from the rectifier 65, after which the excitation of coil 25 causes the dynamometer D to come into play, acting as a governor brake and finally resisting further increase in.

speed. The lower the slider on the resistor 13 is located, the lower will be the voltage of the rectifier 55 at whichcurrent flows through the generator field 8| and the higher will be the excitation of dynamometer coil 25. The result will be a lower ceiling on motoring speed. Thus the rectifier 19 provides a reference voltage as determined by the resistor 13.

In view of the above it will be seen that an upper limit is placed upon the speed of the shaft II when driven by the motor M, as predetermined by the resistance 13. It will be understood that while the engine which is driven from shaft II is being motored by the motor M that the motoring torque reaction is registered through the case I on the scale l3. This provides means for determining friction horsepower.

The purpose of the additional shunt circuit 85 and adjustable resistance 15 is slightly to change the reference voltage when the device is used for motoring when, of course the eddy-current dynamometer D is much less loaded.

When the ignition of the engine is closed and the throttle opened, the dynamometer D will absorb the full load of the engine which may be from ten to twenty times the load applied to it from the wound rotor motor M. Thus the reference voltage is automatically dropped when the device is operating as an energy-absorbing unit and this voltage is raised when the device is being operated as a motoring unit. For example, let it be assumed that a 25 R. P. M. speed increase is required to change the excitation in the coil 25 of dynamometer D from zero value to full value while being driven from the engine. The speed of the dynamometer will normally change slightly from say one-tenth load to full load. Assume that when motoring the dynamometer load is onetenth of normal and when absorbing it is normal. This would require of the order of 22 R. P. M. or so difference in speed at the torque-balancing point of the dynamometer. This is referred to as the governing speed. If it is desirable to motor a friction test at exactly the same speed as the machine had when absorbing engine power, the resistance 15 is adjusted to bring this about, the switch element 8! operating automatically to cut the adjusted resistance 15 into and out of circuit. Thus it can be arranged by adjusting resistance 15 so that when a change is made from absorbing to dynamometer operation, no substantial speed change will occur.

It should be observed that the driving action of motor M on dynamometer D, and the brake action of dynamometer D, while motoring, balance out reactively on the case 1. Hence no error due to the speed limiting action of the dynamometer D is introduced in torque measurement during motoring. The net reaction on case 1 while motoring is that due to the idling resistance of the engine connected to shaft II.

The motor M may also be used for starting the engine by closing the switch 99, which causes closing of the switch 49 and motoring operation. Then after the motor is turning, the switch 99 is opened while the ignition circuit I will be closed and the motor started.

It slfould be noted that the invention, so far as the control of motor M is concerned, has broader implications. The case I may be fixed by means other than a dynamometer scale, for example locked to the pedestals l. Such a construction would amount to an eddy-current absorbing member or brake coupled to a wound-rotor motor. In such a case the eddy-current brake could be in a separate unit coupled to the motor drive shaft II. The brake element would simply be for close motor control. In the case of the example above suggested, if the rheostat 45 were capable only of adjustment to 100 R. P. M. intervals of motor speed, the eddy-current brake control would be used to obtain finer speed control of the motor. For example, if the rheostat 45 could only control motor M to say 800, 900, 1,000 etc., R. P. M., the control of the rheostat 13 would effect further speed control between 800 and 900 R. P. M. through the braking action of unit D. For this purpose it makes no difference whether the unit D is acting as what is called an eddy-current brake or an eddy-current dynamometer, the two amounting to the same thing so far as brake control action on the motor is concerned. The duty of the eddy-current brake or dynamometer is then to reduce the motor speed a small percentage throughout the range that it is impossible to control speed from the rheostat 45.

This phase of the invention should not be confused with any attempts to superimpose a brake control for speed control of a motor where the brake is of the hydraulic or friction type. Such braking control is not satisfactory but the present electrically controlled eddy-current brake control is, because such is capable of providing the necessary control over the smaller increments over which a rheostat such as 45 is not capable of control. Although it is true that the eddy-current brake control dissipates-some energy in the control process, practically this is very small. For example, if the rheostat 45 were capable of a setting to hold the motor M at 900 R. P. M. and another adjacent setting at 800 R. P. M. the brake control would need only to dissipate a small amount of energy in order to bring the speed down from a 900 R. P. M. setting of the rheostat 45 to a desired motor speed of say 850 R. P. M. Thus the invention also .provides in general means for controlling the speed of a wound-rotor motor to a greater degree of accuracy than is obtainable with ordinary stepped resistance rheostats. It also provides a greater degree of stability at a given speed when subjected to changes in load.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As many changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained inthe above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. In an electric motoring dynamometer for engine testing, a rocking casing, a rotary shaft therein, a dynamometer element and a motor element each having a. rotor on said shaft and a stator connected to the casing, a field coil for the dynamometer element, a D. C. circuit connected with said field coil, a D. C. generator connected with the D. C. circuit for exciting said coil, an exciter coil in the D. C. generator, a circuit for said exciter coil. a rectifier feeding said exciter coil circuit, an A. C. generator driven by the shaft and supplying said rectifier, a second rectifier connected in voltage opposition with said first-named rectifier through an adjustable by-pass resistance whereby an adjustable refer ence voltage may be set up against flow of current through said exciter coil circuit, a shunt circuit connected around a part of said by-pass resistance for passing current through the exciter coil circuit more easily than through the bypass resistance, a motor switch controlling excitation of the motor element, an ignition switch controlling ignition of a. test engine connected to the shaft, a shunt switch for said shunt circuit,

and means for substantially simultaneously opening the motor switch and closing said ignition and shunt switches, and for closing the motor switch and substantially simultaneously opening the ignition and shunt switches.

2. In an electric motoring dynamometer for engine testing, a rocking'casing, a rotary shaft therein, a dynamometer element and a wound outside-resistance slip-ring induction motor element, each element having a rotor on said shaft and a stator connected to the casing, a field coil for the dynamometer element, a D. C. circuit connected with said field coil, a D. C. generator connected with the D. C. circuit for exciting said coil, an exciter coil in the D. C. generator, a circuit for said exciter coil, 9. rectifier feeding said exciter coil circuit, an A. C. generator driven by the shaft and supplying said rectifier, a second rectifier connected in voltage opposition with said first-named rectifier through an adjustable by-pass resistance whereby an adjustable reference voltage may be set up against flow of current through said exciter coil circuit, a shunt circuit connected around a part of said by-pass resistance for passing current through the exciter coil circuit more easily than through the by-pass resistance, a motor switch controlling excitation of the motor element, an ignition switch controlling ignition of a test engine connected to the shaft, a shunt switch for said shunt circuit, and means for substantially simultaneously opening the motor switch and closing said ignition and shunt switches, and for closing the motor switch and substantially simultaneously opening the ignition and shunt switches.

3. A motoring dynamometer comprising a rocking case for measuring torque, a rotary shaft in the case having means for attaching an engine to be tested, a dynamometer element having a stator attached to the case and a rotor attached to the shaft. a motor element having a stator attached to the case and a rotor attached to the shaft, a field coil for exciting the dynamometer element, means for exciting said field coil including a first D. C. circuit, means driven by the shaft for delivering current to said D. C. circuit under a potential according to the velocity of the shaft, adjustable resistance means in said first D. C. circuit, a second D. C. circuit connected in voltage opposition with said first D. C. circuit and through said adjustable resistance providing a reference voltage, a shunt circuit across part of said adjustable resistance, a first switch controlling operation of the motor, a second switch controlling operation of the engine as a prime mover, a third switch controlling said shunt circuit, and means including a fourth switch adapted in one position of the fourth switch substantially simultaneously to close the motor switch and open the second and third switches, said fourth switch when in its other position being adapted substantially simultaneously to open the first switch and close the second and third switches.

4. A motoring dynamometer comprising a rocking case adapted for torque measurement, a rotary shaft in the case adapted for attachment to an engine under test, a dynamometer stator attached to the case, a dynamometer rotor attached to the shaft, an induction motor stator attached to the case, a rotor for said motor attached to the shaft, said rotor of the motor having an outside variable resistance circuit and its stator being supplied with A. C. an A. C. generator driven from said shaft, a first rectifier energized by said generator, a rectified D. C. circuit supplied by said first rectifier, a field coil for said dynamometer, an exciting generator for said field cell, an exciting field for said generator supplied by said D. C. circuit, an A. C. supply circuit for the induction motor, a second rectifier supplied by said A. C. supply circuit, a second D. C. circuit supplied by said second rectifier and connected in voltage opposition with said firstnamed D. C. circuit, adjustable resistance means between said circuits, a shunt circuit across a portion of said resistance means, a first switch in the induction motor A. C. circuit, a second switch controlling operation of the engine, a third switch in said shunt circuit, and a fourth switch adapted to close the first switch while opening the second and third switches or to open the first switch while causing closing of the second and third switches.

MARTIN P. WINTHER.

REFERENCES CITED The following references areof record in the file of this patent:

UNITED STATES PATENTS Number 

